1. Field of the Invention
The invention relates to a driving circuit and a lighting apparatus. Particularly, the invention relates to a constant current driving circuit of light emitting diode (LED) and a lighting apparatus.
2. Description of Related Art
Since a light emitting diode (LED) has a small volume, low power consumption and high durability, products using the LEDs as light sources become popular as processing techniques gradually become mature. Since a tiny change of bias may cause a significant change of an operating current within an operation range of the LED, the LED has to be driven by a constant current; otherwise, once the current exceeds a rated value, the LED is probably damaged.
According to a conventional method for driving the LED, a control signal output by a control chip is generally used to turn on/off a switch coupled to the LED. Further, when the control chip detects that a current flowing through the LED is excessively high, the switch is turned off by the output signal, and the current flowing through the LED is gradually decreased along with energy dissipation. However, since the signal transmission takes time, which causes a phenomenon of propagation delay, when the control chip detects an abnormal current, the control chip cannot immediately turns off the switch, so that only after a period of delay time, the abnormal current flowing through the LED can be controlled, and once an operating frequency of the LED is varied, the effect of driving the LED by the constant current cannot be achieved, which may cause damage of the LED after long time utilization.
Therefore, it is a development trend to provide a constant current driving technique of the LED.